The field of the invention is deep well pumping wherein a mechanism is provided at the top of the well which supports and drives a long pump rod extending down the well pipe to a driven reciprocating piston and valve mechanism at or near the bottom of the well. Each stroke of the rod lifts a quantity of oil or other fluid out of the top of the well equal to the volumetric displacement of the driven piston per stroke. On the return stroke the valve at the bottom of the well opens to permit more oil or other fluid to enter above the driven piston. On each pump stroke the entire column of oil in the well pipe is lifted by the rod and driven piston at the bottom of the well.
The pump rod may be vertically reciprocated mechanically as has been done with rocking beam lift pumps for many years or may be vertically reciprocated with a large hydraulic cylinder and piston located at the top of the well. The hydraulic cylinder lift pump is a more recent device. A hydraulic lift pump assembly typically comprises a large vertically mounted hydraulic well lift cylinder placed directly over the well pipe with the cylinder piston rod connected to the pump rod extending down the well pipe. Adjacent and below the well cylinder is a gas engine or electrically driven hydraulic pump.
The hydraulic pump in the pumping mode supplies high pressure hydraulic fluid to the lift cylinder to raise the piston. The hydraulic pump is then shifted to the non-pumping mode and the high pressure flow to the well cylinder stopped thereby allowing the well cylinder piston and the pump rod to fall. An orifice in the lift cylinder supply line prevents free fall of the pump rod on the return stroke.
The pump rod and column of oil contained within the well pipe store a significantly large amount of potential energy as the well cylinder piston moves upwardly on the pump stroke. This stored energy is lost on the return stroke. With a view toward retrieving as much of the lost energy on the return stroke as possible to thereby increase the overall efficiency of the hydraulic well pump system, applicant has developed the energy storage apparatus described below.